the Cause of coloured concentric Rings. 301 
It has also been shown that the blue bow-streaks are seen by re- 
flection, and those of the red bow by transmission * 
In a lens we may at the same time see, in half the set, the 
colours of the reflected, and in the other half, the colours of 
■ the transmitted rings.-f 
And in a prism held before an open window, when the eye is 
close to it, and when half the bow falls on the side of the room, we 
may see blue streaks by ref ection from half the blue bow, and green 
streaks by transmission from half the red bow. £ 
When deep convex, or concave glasses, are laid upon the 
first surface of a lens, the rings are not affected by it.§ 
And when the same glasses are laid upon the first surface of a 
prism the streaks remain unaltered. || 
When the convexity of the lens, which is placed on the 
reflecting surface, is changed, the size of the rings is also 
changed. 
And when the angle of the prism is increased or diminished, the 
distance of the streaks undergoes a proportional alteration 
When the lens is pressed upon the plain glass, the rings 
increase in diameter.-f -f 
And by a pressure of the plain glass against the prism the dis- 
tance of the streaks grows larger. 
To form rings by a lens, scattered light is only required. 
And the same light is best for the production of streaks by & 
prism.§§ 
Many other instances of similarity might be adduced, but 
* See the 43d article. f See the second paragraph in the 1 8th article. 
J The experiment has been made, though not mentioned in this paper. 
§ 9 kee the sixth paragraph of the 24th article, 
|| See the second paragraph of the 46th article. 
See the first paragraph of the 7th article. 
** See the fourth paragraph of the 42d article. 
ff See the 8 th article. See the seventh paragraph of the 24th article. 
§§ See the third paragraph of the 46th article. 
Rr 
MDCCCIX. 
